Rich-

You should do quite well with the Goex powder.
I'm guessing you'll find a load that hits as hard as your old load did, which is as accurate or more accurate than with your old powder.
I run it in a .50 flintlock and a .54 caplock -- on the hot side of the load spectrum I'm getting excellent accuracy and a very very clean burn. The fouling is minimal and soft.

Both of those rifles seem to like thick patching, which ends up holding a good amount of patch lube -- great for use on hunting or field trips that take you into the woods for days at a time. I'm able to run the rifle without having to do a full wet cleaning at night, never had a problem with corrosion.
I'm running roundball too.

Another great feature of the Goex (as it's easier to find and it's cheaper) is that you'll end up shooting more!

Cheers
Tinker